Carburetors are well known devices for mixing gasoline and air together and for supplying this fuel/air mixture to the combustion chambers of an internal combustion engine. Often, the carburetor is used on the engine powering a motor vehicle, such as an automobile or motorcycle, though carburetors are used on non-vehicular internal combustion engines as well. One traditional carburetor is known as the "butterfly" type. This name comes from the shape of the pivotal throttle plate or throttle valve located inside the carburetor body which somewhat resembles a butterfly. Thus, the throttle plate is also sometimes referred to as the butterfly valve.
A butterfly carburetor includes a carburetor body which is secured to the intake manifold of the engine. The carburetor body includes an airflow passage in which incoming atmospheric air is mixed with fuel prior to being admitted to the intake manifold. The throttle plate is located within and generally at the end of the airflow passage which is closest to the intake manifold. A venturi section in the airflow passage is located upstream of the throttle plate. A first fuel jet is located in or adjacent the venturi section so that air passing through the venturi section will draw fuel out of the first fuel jet to mix such fuel with the air flowing through the venturi section. This mixture of atomized air flows past the throttle plate, through the intake manifold, and into the cylinders of the engine, where it is ignited and burned in a known manner.
The amount of fuel and air admitted into the engine is regulated primarily by the operation of the throttle plate. As the operator steps upon or otherwise actuates the throttle, the throttle plate pivots to a more fully open position, increasing the amount of air flowing through the venturi section which correspondingly increases the amount of fuel being sucked out of the first fuel jet. Conversely, pivoting the throttle plate to a more closed position will decrease the total air flow and fuel being supplied from the first fuel jet, to thereby decrease the engine speed. This operation of the throttle plate is sufficient to adequately supply the engine with fuel during idling and cruising operations of the engine.
However, at certain times, additional power is required from the engine. For example, sudden acceleration and high speed operation of the engine requires more fuel than the pivotal throttle plate and first fuel jet combination described above can provide. Accordingly, some carburetors of this type are also provided with a second fuel jet located in the carburetor body for admitting additional fuel to the airflow passage to enrich the mixture and cause the engine to provide more power.
A butterfly carburetor of the type described above, built in various models, has been manufactured and sold for some time by S&S Cycle for use on motorcycles. For example, S&S has previously manufactured and sold a Super B Gas Carburetor. This carburetor is a butterfly carburetor of the type described above and has both the first fuel jet for idling and cruising conditions and the second fuel jet for acceleration and high speed operations. In the parts materials distributed by S&S relating to this carburetor, the first fuel jet is referred to as the "intermediate jet" and the second or high speed jet is referred to as the "main jet". The main jet is mounted on the end of an elongated cylindrical body, referred to by S&S as the "main discharge tube", which conducts the fuel into the carburetor body. Thus, the main discharge tube and main jet when coupled together form a fuel discharge assembly for high power operations.
In the S&S Super B carburetor just described, the main discharge tube has a threaded boss at one end into which the main jet is threaded to couple the two together. The main discharge tube has an elongated hollow bore extending from the threaded boss all the way through to the other end of the tube. Fuel flows from the main jet into the interior of the discharge tube and through the hollow bore until the fuel is squirted out of the end of the discharge tube. The discharge tube is provided with a line of small holes or openings for admitting air and helping provide proper fuel atomization.
In examining this fuel discharge assembly, the Applicant noticed that the inlet to the hollow bore in the discharge tube is spaced from the main jet by a substantial distance, i.e. by a quarter of an inch or so. Thus, a cylindrical pocket was found by the Applicant to be formed between the outlet end of the main jet and the inlet to the bore of the discharge tube. Applicant felt that such a pocket could possibly allow the fuel to tumble or swirl in the pocket before entering the bore in the discharge tube.